This invention relates to a xerographic reprographic system wherein the document to be copied is scan/illuminated by a linear illumination lamp, and more particularly, to a method for initially aligning the lamp so as to provide an initial optimum level of performance.
In a document reproduction system which incorporates a scanning optical system (moving illumination source, reflectors, mirrors, projection lens) to project an image of a document onto a photoreceptor surface, the exposure of a point on the photoreceptor is equal to the total irradiation received by the point as it scans through a slit. When a uniform density document is being imaged, a uniform exposure of the photoreceptor is desired. An optimum exposure level is initially set for each system at the time the particular reproduction system is manufactured and assembled.
Typically, the document illumination lamp is fixedly mounted in the proper location beneath the platen. Since the light output of the lamp used varies with the rotational position of the lamp, some method must be used to determine the rotational position which will produce the optimum exposure level at the image plane after being transmitted through the system optical path (projection lens, and scan and folding mirrors). The conventional method has heretofore relied on repeated trial and error techniques, wherein the lamp is incrementally moved or rotated and a series of illumination readings are taken at the image plane by a light detector, each reading being compared with other readings until an acceptable level within a preset tolerance range identified.
When an acceptable reading is obtained, the alignment of the lamp is set at the position which provides the acceptable light level reading. A problem with this prior art technique is that while the final lamp alignment may be within specification, it may not be the most optimum rotational position. Another disadvantage is the time consuming methodology which is used.
It would be desirable to initialize lamp performance more quickly and to select the position which will produce optimum performance, not merely within spec performance. According to a first aspect of the present invention, the lamp illumination output reflected from the platen and transmitted through the optical system is directed to a linear photosensor array positioned at the image plane. Illumination profile data is amplified and recorded by a computer controlled data acquisition device. Software operated within the computer calibrates all data acquisition, and provides graphical displays of calculated illumination characteristics on a display screen. An operator can change the rotational position of the illumination lamp relative to the reflector through an entire 360.degree. rotation while viewing the display screen to select the optimum position as indicated by a displayed bar graph or, alternatively, while viewing a displayed axial illumination profile.
According to another aspect of the invention, the screen display can be used to select and adjust an infrared densitometer to correct for differences in illumination lamp, infrared densitometer sensitivity, and patch densities.
The following prior art references are believed to be of interest:
U.S. Pat. No. 4,464,681 to Jacobs et al. discloses a method and apparatus for adjusting a facsimile document scanner wherein a test pattern is scanned by an array of photodiodes to detect optical path misalignment. The output from the photodiode is displayed on an oscilloscope. A user can then move the photodiode array to adjust the optical path. FIG. 5 shows the photodiode output for a perfectly aligned device. See Col. 4, lines 11-57.
U.S. Pat. No. 4,943,834 to Maeda et al. discloses an image forming apparatus capable of detecting, analyzing and displaying spectroscopic color data of an original wherein an array of sensors is used to detect color data which in turn is used for determining the amount of toner needed for a particular color image. Once an image is scanned, the color characteristic of that particular image are displayed to an operator so that adjustments can be made before a copy is produced. See Col. 4, lines 18-29.
U.S. Pat. No. 4,467,364 to Konagaya discloses a device for measuring tone correction wherein tone density is analyzed and displayed as a correction curve on a monitor. A user can then adjust a tone control circuit as a monitor is observed in order to correct any errors. See Col. 2, lines 39-49. A television camera is used for scanning an image.
Also of interest is copending application U.S. Ser. No. 07/590,425, filed Sept. 28, 1990 and assigned to the same assignee as the present invention. This application discloses a diagnostic test process for a visual verification of the spatial illumination characteristics of an illumination system used in a raster input scanner (RIS) printing system.
More particularly the invention is directed toward a method for providing initial optimized performance of an illumination and exposure system used to form a latent image at an exposure station of a document on a photosensitive medium, including the steps of:
introducing a linear photosensitive display consisting of a
plurality of photodiodes into said exposure station,
energizing an illuminator to produce a light output which is transmitted through said exposure station and is incident along the length of said array;
converting the output of the photosensitive array into video signals representative of the average illumination output of the illuminator,
providing a bar graph on a display screen of said average illumination error superimposed against a horizontal specification line on said display representing a maximum acceptable illumination level, and
positioning said illuminator while observing said bar graph and selecting that alignment position of the lamp at which the bar graph is at a minimum value relative to said specification line.